Osteoarthritis is the most common rheumatologic disease in humans. New pharmacologic and surgical treatments are creating a demand for non-invasive techniques capable of detecting this disease at its earliest stages. We believe that studying the dynamic behavior of articular cartilage to mechanical stress may yield greater diagnostic information than images of cartilage in a non-stressed state. For this reason, we employ MRI to observe articular cartilage in-vitro during deformation. During the past year we have found that articular cartilage responds in a biexponential fashion to physiological compressive loads. We are currently testing the hypothesis that this biexponential response corresponds to two distinct layers in cartilage, as our magnetization transfer maps of articular cartilage show a bilayered structure. Additionally, we are using sodium NMR spectroscopy to investigate the osmotic behavior of articular cartilage during compression, as the mechanical properties of articular cartilage arise from the strong osmotic effect of sodium cations electrostatically attracted to proteoglycan sugar residues.